The impetus to recycle increasing amounts of various printed paper streams has become a worldwide event. This is especially evident in areas, like North America, where this approach has not been widely practiced. For some grades, such as old corrugated cardboard, the rate of recycling in the U.S. is now greater than 50%.
Some of the higher quality grades, including mixed office waste have not shown the same rate of reuse and therefore present a severe disposal problem. This is due to the difficulty of removing polymeric inks, coatings, and toners such as non-contact, fused laser printer inks, xerographic toners, UV/EB cured inks, varnish overlays, and coated papers. Chemical deinking agents, e.g., sodium hydroxide, sodium silicate, and hydrogen peroxide, may not work well for laser ink and xerographic toner removal. Specifically, there may be solubilization of the calcium filler at higher pH values. Mechanical dispersion of coatings, non-contact toners, and inks involves both high capital and operating cost. Additionally, irreversible changes in pulp fiber chemistry can occur where a significant proportion of mechanical pulp fiber is included in the furnish.
Enzymes have been used in the prior art to improve the deinking process in xerographic paper, laser printed paper, old magazines, and old newsprint. See, for example, PCT WO 91/14819 (old magazines and newsprint-basic pH); Jeffries et al., 1994, Tappi Journal 77:173-179 (xerographic and laser-printed paper); Kim et al., Proceedings of the 1991 Tappi Conference, pp. 1023-1030 (old newsprint-acidic pH); Prasad et al., 1993, Appita 46:289-292 (xerographic and laser-printed paper); and Prasad et al., 1993, Nordic Pulp and Paper Journal 2:284-286 (old newsprint).
However, each of the above-cited references used only multicomponent cellulases, which contain various types of enzyme activities. No other alternative has ever been considered. The use of multicomponent cellulases poses a number of disadvantages. First, these multicomponent cellulases contain a wide variety of enzymatic activities, many of which are unnecessary for deinking. These unnecessary enzymes may cause unwanted degradation reactions and potentially cause yield loss and reduce the fiber strength of the pulp. Second, batch to batch variations will often occur when fusing native multicomponent enzymes where standardization must be based on a joint characteristics. Third, since multicomponent cellulases may only be isolated from microorganisms, it is rather costly to isolate these cellulases; recombinant DNA methods are not applicable.
Therefore, a need exists for an improved deinking process for printing and writing grade printed papers containing for example, laser inks and xerographic toners and for newsprint. It is therefore an object of the invention to provide a method for economically recycling high quality printed papers and newsprint.